I don’t see the testers relationship of seat belt mounts to side sills, unless I’m missing something. Floor pan in a bad state? It sounds as if the sills repair is the major concern, as may be the chassis rail, with the floor pan also suspect. If the front chassis frame is also suspect, then you are looking at a big repair bill. Obviously time for a rethink, as you are doing. Point is, if yo decide to stay with the MX5 route, then you can pay up to ten thou or more for a good example, so you have the difference between that sum and your car’s present value (Ouch moment - a lot less than one thousand) to play with. You need to find a good repairer, who may not be in your area, so can you afford to be without a car for a month or two - may be longer?
On the other hand, a good repairer may offer you a one year guarantee against their workmanship and material, but not on the rest of the car, and rust being perfidious, you have no idea where the next part will fail, in which case- money spent - money wasted. As it stands, you car is worth peanuts at a crapper, but in pieces, worth a lot more. If you have the time, space and energy, consider breaking it up yourself and offering parts for repair, , but yes, I know that’s easier said than done. For the sake of time, space and energy, you could even consider breaking the car, buy a good kitcar and make your own roadster for less than the price of a new car, again, easy said!
Last, but no least - there are all kinds of cars on car lots these days, you can buy later models offering more comfort than an MX5 for the money you’ll save on repairs now and in the future, frankly, that’s the direction I’d go, but you need to make your own decisions, based on what you feel, not on what we say. Good luck.
